(a) Field of the Invention
The present invention relates to an organic-inorganic nanocomposite and preparation thereof, and particularly to an organic-inorganic nanocomposite capable of uniformly dispersing layered silicates in a polymer medium, and preparation thereof.
(b) Description of the Related Art
Generally, a method of mixing inorganic substances is used for synthesizing a polymer having high strength and high rigidity. In this method, as an added inorganic substance, a plate-shaped or a vinyl-shaped substance is more appropriate for improving physical properties than a globular one because it increases surface area per unit mass. For this reason, various efforts to intercalate polymers into layered silicates have been attempted. Recently, U.S. Pat. No. 4,810,734 disclosed an organic-inorganic composite using layered silicates and nylon, and as physical and thermal properties thereof have been improved, studies of nanocomposites have attracted further attention.
It is regarded that the degree of exfoliation of a layered silicate primarily influences the improvements of the physical properties of a polymer by an organic-inorganic nanocomposite. However, it is not an easy task to completely exfoliate the layered silicates in the polymer medium because of low compatibility between them. Therefore, in order to solve the problem, many studies for dispersing layered silicates in a polymer medium have been attempted.
In U.S. Pat. No. 4,889,885 and Macromolecule 2000, 33. 2000˜2004, Polymer 1994, 35, 3296˜3304, sodium ions or potassium ions of layered silicate were ion-exchanged with a cationic compound (organosilane compound having alkylammonium ions or appropriate functional groups) to make organoclay, and the distance between layers was widened and then appropriate monomers were added to polymerize, or it was melt-intercalated to cause exfoliation. However, there was a problem in that the degree of exfoliation differs depending on the polymers to be intercalated.
Recently, results of synthesis of nanocomposites wherein layered structures of silicate were exfoliated in polymer media through introduction of organophilic intercalants having reactive groups and subsequent polymerization have been announced. However, with these methods it is difficult to produce a polymer because sufficient radicals and monomers cannot be continuously provided into the layered structure, and even if produced, there is a limit on exfoliation of the layered silicate because the molecular weight and the structure cannot be controlled.
Recently, the Sogah group synthesized a polystyrene-inorganic nanocomposite with a significantly improved exfoliation degree by intercalating nitroxide in which ammonium substituents were introduced into a layered silicate, and by introducing living polymerization inside the inorganic substance (J. Am. Chem. Soc 1999, 121. 1615˜1616). However, this method has the disadvantage of only being applicable to some limited monomers, and it requires high temperature conditions. Additionally, Moad et al have synthesized dithioester compounds and shown that the living polymerization method can be applied to various monomers (Macromolecules 31, 5559(1998), WO 98/01478, WO 99/05099, WO 99/31144, WO 00/35177), but studies of preparation of organic-inorganic nanocomposites using the same are totally lacking.
Accordingly, there is a need for study of preparation of organic-inorganic nanocomposites capable of uniformly dispersing layered silicates in various kinds of polymer media.